1. Field of the Invention
This invention relates to electromagnetic solenoid actuators having rapid response time and extended stroke. More particularly, the invention relates to actuators having multiple electromagnets for attracting a telescoping armature.
2. Prior Art
Solenoid actuators are known in the art. These actuators often comprise a movable armature maintained in a spaced relationship from an electromagnet. The distance therebetween, called an air gap, thereby defines the stroke of the armature. It is desirable to obtain a fast acting actuator having a long stroke. However, increasing the stroke implies a larger air gap which further implies developing a greater magnetic field to produce the requisite force to attract the movable armature. One method of developing these larger forces is to increase the size of the magnetic circuit; requiring a larger stator, coil and armature as well as requiring larger excitation currents. However, these larger units often take a greater time to build up or energize and de-energize the required magnetic field. Similarly, the response time of the armature is slowed because of its increased mass or inertia. It is not possible, however, to fully compensate for these longer response times merely by increasing the level of exciting current, and that the increased currents may only produce excessive local heating and power usage.